1. Field
The present invention relates to an assembly of an integrated device, which enables a facilitated fluidic connection from outside to regions of the device. In particular, the following description will make explicit reference, without this implying any loss in generality, to a pressure-sensor device of a differential type.
2. Description of the Related Art
As is known, in the field of electronics, the use of silicon-microprocessing techniques for making microelectromechanical structures (so-called MEMS) is increasing.
For example, known to the art are pressure sensors, operation of which is based upon detection of a deformation of a membrane suspended over a cavity, microphones, and gas sensors, all of a MEMS type.
Also known are microelectromechanical structures providing complete analysis systems in a chip made of semiconductor material (the so-called LOC—Lab On Chip). These structures comprise in general one or more of the following elements: electrodes; reservoirs for exchange solutions or for waste solutions, or for reagents or other fluids; reaction chambers; channels for separation or conveyance of fluids; and optical interfaces.
Since the dimensions of MEMS devices are particularly small, for example less than 1 mm×1 mm×0.5 mm (length×width×thickness), traditional packaging techniques, and in particular molded or pre-molded packages of a traditional type, do not prove advantageous. Optimized packaging techniques for MEMS devices have consequently been developed, amongst which the so-called “wafer-level packaging” technique, which envisages formation of a protection layer directly on a layer of semiconductor material housing integrated devices.
For example, in the patent application EP 05425719.1 filed on Oct. 14, 2005 in the name of the present applicant, a package for an integrated device made using MEMS technology is described.
In detail (FIG. 1), an integrated device 1 (in particular a differential pressure sensor) comprises a device substrate 2 having a top surface 2a; within the device substrate 2, in particular at two distinct surface portions thereof, a first pressure sensor 3 and a second pressure sensor 4 are formed. Each pressure sensor 3, 4 comprises a buried cavity 5, which is separated from the top surface 2a by a membrane 6; the membrane 6 is flexible, deformable, and suspended over the buried cavity 5. The buried cavity 5 is isolated from, and entirely contained within, the device substrate 2. Transducer elements 7, for example piezoresistors, are arranged inside the membrane 6, detect deformations of the membrane 6 (due to an applied pressure), and generate corresponding electrical signals.
The integrated device 1 further comprises a capping substrate 10, made of semiconductor material (for example silicon), glass, or other ceramic or polymeric material, which is mechanically coupled to the device substrate 2, above the front surface 2a, so as to cover and protect the first and second pressure sensors. The capping substrate 10 is coupled to the device substrate 2 via a bonding process, which exploits a sealing region 13, set in contact and on top of the front surface 2a to ensure bonding. The sealing region 13 surrounds, without being superimposed thereon, the respective membrane 6 of the first and second pressure sensors 3, 4. In addition, the capping substrate 10 has a first sensor cavity 14 and a second sensor cavity 15, separate from one another in a fluid-tight manner and arranged above, and in communication with, a respective membrane 6 of the pressure sensors, and a first entry region 16 and a second entry region 17 for accessing the first and second sensor cavities 14, 15 from outside the capping substrate 10.
Input/output electrical connections are provided for electrical connection of the pressure sensors 3, 4 with the outside, for example in the form of connection pads 18, which are carried by a portion of the front surface 2a set outside the sealing region 13 and the capping substrate 10, and which can be contacted using the wire-bonding technique.
The integrated device 1 further comprises a package 20, of a land-grid array (LGA) type (as shown in FIG. 1), or ball-grid array (BGA) type (in a way not illustrated), which englobes the assembly constituted by the device substrate and the capping substrate. In detail (see also FIG. 2), the device substrate 2 is joined, via an adhesion layer 21, to a base body 22, for example, a multilayer organic substrate, defining the base of the package 20. A coating 24 of plastic material, for example comprising resin, obtained via a mould of appropriate shape and size, covers the integrated device laterally, but not the outer surface of the capping substrate 10 (i.e., the surface not in contact with the device substrate 2), which forms part of a first outer face 20a of the package 20. In this way, the first and second entry regions 16, 17 remain free and exposed from the outside of the package 20 (as is clearly evident from FIG. 2) so as to enable inlet of fluids, a difference of pressure of which is to be determined, inside the integrated device. Through connections 25, made through the base body 22, connect the connection pads 18 to external contact pads 26 of metal material, carried by an outer surface of the base body 22, defining a second outer face 20b of the package (as is known for the LGA technique). The dimensions of the package 20 are in this way particularly small, for example in the region of 5 mm×5 mm×1 mm.
As shown in FIG. 3, the package 20 can further house an ASIC (Application-Specific Integrated Circuit) die 27 made of semiconductor material, integrating an ASIC and electrically coupled to the integrated device 1. The ASIC die 27 is joined to the base body 22 via a respective adhesion layer 21, laterally to the integrated device 1, and is surrounded by the coating 24. Electrical connections (e.g., electrical wires) connect (for example, via the wire-bonding technique) the ASIC die 27 to the integrated device 1 and to the through connections 25 for connection to the outside.
Differential-pressure-sensor devices are also known, as described for example in US Patent Publication No. 2006/0260408 filed on May 4, 2006 and assigned to the same assignee of the present application, which are configured so as to provide a lateral access to the substrate in which the pressure sensor is integrated. In particular, a connection channel, buried inside the device substrate, extends laterally with respect to the buried cavity 5 and is in fluidic connection with an internal surface of the membrane 6. The device substrate is processed in an appropriate way (for example, with back-end techniques) so as to enable lateral access to the connection channel, and hence access to the buried cavity. The membrane 6 is thus deformed as a function of a difference in the pressures that act on its external and internal surfaces.
In the above case (FIG. 4), the integrated device 1 comprises just one pressure sensor 3 integrated in the device substrate 2, so that the capping substrate 12 has only a first entry region 16 for access to the corresponding membrane 6. A second entry region 17 is provided at the side of the package 20 in an outer side face 20c thereof adjacent to (i.e., having a side in common with) the first outer face 20a so as to traverse the coating 24 and reach the buried connection channel.
The microelectromechanical devices and structures described all require an interaction with the outside world, for example, for inlet of fluids, the pressure of which is to be determined (as in the case of pressure sensors), or else which have to undergo analysis or desired treatments (as in the case of LOCs). For this reason, fluid-introduction elements, for example ducts of appropriate shape and size, or else other introduction means (for example syringes, in the case of LOCs), must be coupled to the integrated devices so as to enable interfacing with entry regions thereof (for example, the aforesaid first and second entry regions 16, 17, set in fluid communication with the deformable membranes of the pressure sensors).
A problem that may arise is due to the fact that the extremely small dimensions of the microelectromechanical devices, and the consequent minimal spacings between the entry regions, can render coupling with the aforesaid fluid-introduction elements extremely difficult. Usually, in fact, the fluid-introduction elements are manufactured using standard technologies (for example, via plastic fabrication processes), and a considerable difference in dimensions exists, that can even be greater by one order of magnitude than the corresponding microelectromechanical structures. For example, the first and second entry regions 16, 17 visible in FIGS. 2 and 4 are set apart from one another by a first distance of separation d1 of 1-1.5 mm, whilst the fluid-introduction elements available and generally used comprise plastic tubes having a cross section of, for example, 3 mm. The problem highlighted is clearly all the more felt the closer the entry regions of the integrated devices are to one another and it is aggravated by the fact that the same regions are arranged on the same surface of the integrated devices (as in the case of FIG. 2) or even on adjacent surfaces (as in the case of FIG. 4). More in general, the aforesaid entry regions are often arranged in such a way as to render far from convenient, or in any case not optimized, the interaction between the outside world and the fluid-introduction elements.